This invention relates to an electrical connector, which will simply be referred to as xe2x80x9cconnectorxe2x80x9d, and in particular, to a connector for use in a high-speed signal transmission system.
In the prior art of a connector for the high-speed signaling or the differential signaling, a connector has a pair of contacts for receiving/transmitting a pair of signals opposite in voltage, that is a pair of positive and negative voltage signals. The differential signaling is often used in the high-speed transmission system in order to achieve excellent noise immunity. The paired contacts will be called a xe2x80x9cdifferential pair of contactsxe2x80x9d. Similarly, the paired signals will be called a xe2x80x9cdifferential pair of signalsxe2x80x9d.
A differential pair of signals are transmitted through a pair of signal lines, for example, a pair of coaxial cables, twin (parallel) coaxial cable, or a twin (twisted) axial cable (twinax cable), from or to a connector. In the case of using coaxial cables, a pair of center conductors, which are center conductors of the pair of coaxial cables (namely, a pair of positive and negative signal lines), are connected to the differential pair of contacts in the connector. A pair of outer conductors of the pair of coaxial cables are bundled and are connected to a ground contact in the connector. In the case of using a twin-(parallel) coaxial cable, the pair of inner conductors of the twin coaxial cable are connected to differential pair of contacts in the connector, while an outer conductor of the twin-coaxial cable is connected to a ground contact in the connector. In use of the twinax cable, twisted twin conductors are connected to the differential pair of contacts, respectively, while a drain line is connected to the ground contact.
It should be here considered that a connector usually comprises a plurality of contacts arranged in rows of contacts and each row may include two differential pairs of contacts. In this case, a single ground contact is generally arranged between two differential pairs of contacts, in order to minimize interference between two differential pairs of signals passing through the two differential pairs of contacts and to minimize the number of contacts in a connector. That is, a differential pair of contacts, a ground contact and another differential pair of contacts are arranged in that order so that the ground contact is shared by the different pairs of contacts. As an example of such pin (contact) assignments, there is an existing connector compliant to the physical interconnect specification of the DVI (Digital Video Interface) made by the DDWG (Digital Display Working Group whose URL is xe2x80x9chttp://www.ddwg.org/xe2x80x9d). Specifically, a connector compliant to the DVI specification supports Transmission Minimized Differential Signaling (TMDS) so that a differential pair of contacts receive/transmit a pair of positive and negative signals, that is, a differential pair of signals, under the TMDS.
The present inventors point out here that the above-mentioned pin assignments are non-symmetric ones and that one contact of a differential pair of contacts is farther than the other of the differential pair of contacts from a corresponding ground contact. In addition, an imbalance on impedance might arise from the non-symmetric pin assignments and, if arising, it makes electrical path lengths of a differential pair of positive and negative signals different from each other because the physical path lengths of the differential pair of signals are usually the same. If there is a large difference in electrical path lengths of a differential pair of signals, a critical difference occurs between transmission delays of the differential pair of signals so that the differential pair of signals do not suitably work any longer. Therefore, an impedance imbalance arising from the non-symmetric pin assignments should be compensated.
Furthermore, it is required that an output impedance of a connector, especially, on every contact is normally predefined in order to make an impedance matching between it and an input impedance of a mating connector on every contact. This requirement has to be met on compensating the imbalance mentioned above.
It is therefore an object of the present invention to provide a connector which can compensate an imbalance arising from the non-symmetric pin assignments while meeting the requirement of an impedance matching.
In accordance with one aspect of the present invention, a connector is provided for connecting at least first and second signal lines and a ground line with a mating connector fitable to said connector, said connector comprising a ground plate (1), an insulator (30), first and second contacts (21) being to be connected with said first and second signal lines, respectively, and a ground contact (22) being to be connected with said ground line, said ground plate (1) being electrically connected with said ground contact (22), said insulator (30) supporting therein said first and second contacts (21) and said ground contact (22) in accordance with predetermined pin assignments where said first and second contacts (21) and said ground contact (22) are arranged in the same row so that said first contact (21, 108) is positioned farther than said second contact (21,107) from said ground contact (22, 106), said connector being characterized by provision of a conductive finger portion (3) disposed in the proximity of and along said first contact (21, 108), said conductive finger portion (3) being electrically connected with said ground plate (1).
Specifically, said insulator (30) has first to third through holes (35) and an additional hole (34), said first to third through holes (35) being arranged in the same horizontal line so as to receive said first and second contacts (21), and said ground contact (22) inserted thereinto, respectively, in accordance with said predetermined pin assignments, said additional hole (34) accommodating therein said conductive finger portion (3) and being located above or below said first through hole (35) in the insulator (30).
Said first and second contacts can be used for receiving and transmitting a differential pair of signals, respectively, and, for example, can be positive and negative, respectively, alternatively, negative and positive, respectively.
Preferably, said conductive finger portion (3) is formed integrally with said ground plate (1).